In a long-term evolution (LTE) system, downlink control information (DCI) is transmitted in a form of a physical downlink control channel (PDCCH) by a base station, and data are transmitted in a form of a physical downlink shared channel (PDSCH) by the base station. Wherein, the PDCCH supports space diversity multi-antenna transmission based on cell-specific reference signals (CRSs), with a maximum number of transmission antennas being 4.
In order to improve data transmission rate and spectral efficiency, multiple antennas are widely used in a wireless communication system. In a long-term evolution advanced (LTE-A) system, a downlink may support up to 8 transmission antennas; however, the PDCCH may only support at most 4 antennas in transmission. In order to further improve performance of a cell-edge user, a coordinated multipoint transmission technology based on a network structure of multiple geographically spaced apart remote radio heads (RRHs) will be widely used in a future wireless communication system. However, as the ability to demodulate a CRS is currently limited, attention is paid to a PDCCH based on a UE-specific demodulation reference signal (DM-RS), where the PDCCH is expanded from previous N orthogonal frequency-division multiplexing (OFDM) symbols to other regions, such as being expanded to a PDSCH region starting from an (N+1)-th symbol.
In such a case, for easy use of the same precoding matrix in the demodulation of the PDSCH, if the ranks of the precoding matrices of the PDCCH and the PDSCH are different, different power allocated for the PDCCH and the PDSCH will result in degradation of the performance of the PDCCH, since the rank of the precoding matrix of the PDCCH is always lower than that of the precoding matrix of the PDSCH. Hence, the power of the PDCCH needs to be increased to compensate for the degradation of the performance. As terminal equipment cannot learn the above change of power, the effect of power on data after channel estimation cannot be eliminated when the terminal equipment receives data and pilots via a wireless attenuation channel, and hence the data cannot be demodulated correctly. There is no solution for such a problem at present.
It should be noted that the above description of the background art is merely provided for clear and complete explanation of the present invention and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background art of the present invention.